I set an ebook on Amazon to $2.99, but when it appears on Amazon, it's 'discounted' to 99 cents. Why is that? And is there any way I can change it?

Amazon retain the right to discount any price to match the price available elsewhere. So, for instance, if you're offering the ebook at Smashwords as well at $0.99, Amazon are allowed to drop the price. (And pay you 70% of ($0.99-delivery fee) instead of 70% of ($2.99-delivery fee.)

If the ebook isn't available anywhere else at less than $2.99, Amazon are still allowed to discount it. But then they still owe you 70% of ($2.99-delivery free).